This study centres on conductive polymers with particular reference to those exhibiting
positive temperature coefficient of resistance (PTC) behaviour. Applications of PTC
polymers are identified including, with special relevance to this study, automotive
The electrical properties and the structure of a particular conductive polymer that has
a carbon black conductive filler and exhibits a positive temperature coefficient
characteristic, have been measured.
Early problems affecting the testing and service performance of these devices are
described. Initial concepts of the factors affecting their structure and performance are
outlined. The importance of the characteristic known as resistance linearity is
described and its important relationship with device performance is noted. The results
of a literature survey are detailed.
Typical materials and manufacturing processes employed for the type of heater circuit
central to this study are described.
The results of initial testing and analysis of PTC heater circuits in relation to
manufacturing process variables, ageing tests and service failure are summarised.
The results of further testing of heater samples and analysis using advanced
techniques including Fourier transform IR spectroscopy (FTIR), Calorimetric analysis
with scanning microscopy (CASM), Auger electron spectroscopy (AES), Static
secondary ion mass spectrometry (SSIMS) and Laser microprobe mass spectrometry
(LIMA) are given.
The structure of the PTC polymer used in construction of the heater circuit is
examined with a high resolution scanning electron microscope (FEGSEM) and the
distribution of the carbon filler is determined. Structural changes and changes in the
distribution of the carbon resulting from thermal conditioning and other stresses are
investigated. A cause of functional failure of heater circuits in service has been
Conclusions have been drawn and further work proposed.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.